Jenny Wegley wades into waist-deep water to guide protective tarps over koi ponds at the Dallas Arboretum. The tarps are to protect the aquatic ecosystems from insecticide sprayed over the city from airplanes to reduce mosquitoes carrying the West Nile virus.

Dallas is now engaged in an air war against West Nile disease-bearing mosquitoes.

Beginning Thursday night, aircraft are flying at low level (300 feet), spraying a mosquito-control product called “Duet.” Officials say the substance – which has been approved for both ground and aerial application by the EPA – is safe, spread in low volume (less than one ounce per acre).

But there is some pushback to aerial spraying, which critics say is not wholly effective (it kills adult mosquitoes but not larva) while also killing beneficial insects, including honeybees, ladybugs, and dragonflies, as well as fish, bats, birds, and geckos that prey on mosquitoes.

But he cautions that “it doesn’t take the place of the basic precautions,” including the use of insect repellent. People in the area also are being urged to drain standing water where mosquitoes can breed and proliferate.

Still, health officials in Dallas recommend that children and pets remain indoors until the spray has dried. That goes for some people with respiratory problems, as well.

Over the years, spraying to kill insects has been a common though sometimes controversial practice.

Into the mid-20th century, DDT was used extensively until publication of Rachel Carson’s “Silent Spring” in 1962 raised questions about the environmental impact – including its carcinogenic effects on humans and its weakening effect on egg shells. The banning of DDT in the US in 1972 was a major factor in recovery of the endangered bald eagle.

In 1981, California Gov. Jerry Brown faced the difficult decision to use malathion spray to control an infestation of the medfly decimating the state’s fruit crops. After some delay in moving from ground to aerial spraying, the infestation was finally halted. But at least one study since then has connected the chemical to instances of ADHD (attention deficit hyperactivity disorder) in children.

Texas officials say the best defense against mosquitoes and the disease they transmit is to practice the “four Ds”: